1. Field of the Invention
The present invention relates to a magnetic material.
2. Description of the Related Art
As high performance rare earth permanent magnets, hitherto, a Sm-Co system magnet and a Nd-Fe-B system magnet are known. Their mass production is currently on a sharp increase.
These magnets contain rare earth elements such as Nd and Sm. The rare earth elements bring about a very large magnetic anisotropy derived from the behavior of 4f electrons in a crystal field. As a result, the coercive force (iHc) is increased. Such high performance magnets are mainly used in electric appliances such as loudspeakers, motors, and other devices.
On the other hand, a great demand has arisen recently for down-sized electric appliances and efforts have been made to provide permanent magnets of even higher performance that can be realized by improving the maximum energy product [(BH)max] of a permanent magnet.
The magnetic material including rare earth elements and Fe or Co is promising. For improving (BH)max, an amount of Fe or Co in a principal phase of the material has to increase, because it causes an increase in the saturation magnetic flux density (Bs).
The present inventors and others have discovered a new magnetic material including a principal phase whose crystal structure is TbCu.sub.7 type or ThMn.sub.12 type, which is described in U.S. patent applications of application Ser. No. 961,821 filed on Oct. 16 in 1992, application Ser. No. 858,014 filed on Jul. 6 in 1993 and application Ser. No. 203,371 filed on Mar. 1 in 1994.
The new magnetic material has a high Bs. Therefore, it is considered that a high performance magnet can be made of the material. However it is difficult to make a magnet having a high (BH)max. In general, a heat treating process is needed to obtain a high iHc and in the heat treating process, however, the principal phase of the material, i.e., TbCu.sub.7 phase, tends to decompose into .alpha.-Fe phase. As a result, the amount of the principal phase is decreased and magnetic properties of the material are deteriorated. Further, the decomposition causes low yield rate of magnets.